A method of manufacturing a graphene fiber is provided. The method includes preparing a source solution including graphene oxide, supplying the source solution into a base solution containing a foreign element to form a graphene oxide fiber, separating the graphene fiber from the base solution and cleaning and drying to obtain the graphene oxide fiber containing the foreign element, and performing thermal treatment to the dried graphene oxide fiber containing the foreign element to form a graphene fiber doped with the foreign element. Elongation percentage of the graphene fiber is adjusted by concentration and spinning rate of the source solution.